1. Field of the Invention
This invention relates to a method of purifying .alpha.-substituted acetic acids.
The .alpha.-substituted acetic acids obtained by the method of this invention, such as 2-(3-benzoylphenyl)propionic acid, have valuable pharmacological properties and are particularly useful as anti-inflammatory drugs.
2. Description of the Prior Art
Japanese Pat. Publication No.8301 ( 1977 ) discloses a process for producing 2 (3-benzoylphenyl)alkanoic acids, which comprises hydrolyzing a 2-(3-benzoylphenyl)alkanonitrile by heating it under reflux in an aqueous methanol containing sodium hydroxide, concentrating the reaction mixture, washing the concentrate with diethyl ether, acidifying the aqueous layer with hydrochloric acid, and collecting the product which separated out by filtration, followed by washing with distilled water and drying.
U.S. Pat. No.4,201,870 discloses a process for producing 2-(3-benzoylphenyl)alkanoic acids, which comprises hydrolyzing a 2-(3-benzoylphenyl)alkanonitrile by heating it under reflux in an aqueous methanol containing potassium hydroxide, concentrating the reaction mixture, washing the concentrate with diethyl ether, decolorizing the aqueous layer with activated charcoal, filtering off the activated charcoal, acidifying the filtrate with hydrochloric acid, extracting the product which separated out with diethyl ether, distilling off the ether from the extract, dissolving the residue in acetonitrile, and decolorizing the solution with activated charcoal, followed by crystallization, filtration and drying.
Japanese Pat. Kokai No.115452 ( 1976 ) discloses a process for producing 2-(3 benzoylphenyl)alkanoic acids, which comprises hydrolyzing a 2-(3-benzoylphenyl)alkanonitrile by heating it under reflux in an aqueous ethanol containing sodium hydroxide, concentrating the reaction mixture, washing the concentrate with dichloromethane, acidifying the aqueous layer with hydrochlcric acid, extracting the product which separated out with dichloromethane, distilling off the dichloromethane from the extract, and dissolving the residue in diethyl ether, followed by crystallization, filtration and drying.
These conventional methods, in which .alpha.-substituted acetic acids are purified in the form of salts with strong alkalis in the light, have the problems that the final products contain colored impurities occasionally assuming dark brown or black color and that their yield is not satisfactory.
In addition, the purification operations are cumbersome and take a long time.